Technics RS-B11W Service Manual page 8

Note :
Before measuring and adjusting, the overall frequency
response make sure of the playback frequency response ( For
the method of measurement, please refer to the playback fre-
quency response).
(Recording equalizer is fixed)
1. Make connections as shown in fig. 11.
2. Place UNIT into normal tape mode and insert the normal
reference blank test tape (QZZCRA).
3. Supply a 1 kHz signal from the AF oscillator through ATT to
LINE IN.
4; Adjust ATT so that input level is - 20dB below standard
recording level (standard recording level= 0 VU).
5. Adjust the AF oscillator frequency to 1 kHz, 50Hz, 100Hz,
200Hz, 500Hz, 4 kHz, 8 kHz, 10kHz and 12. 5 kHz signals,
and record these signals on the test tape.
6. Playback the signals recorded in step 6, and check if the
frequency response curve is within the limits shown in the
overall frequency response chart for normal tapes (fig. 10).
(If the curve is w ithin the charted specifications, proceed
to steps 7, 8 and 9.)
If the curve is not within the charted specifications, adjust
as follows;
Adjustment (A) :
When the curve exceeds the
overall specified frequency
response chart (fig. 10) as
shown in fig. 12.
1) Increase bias current by
turning VR9 ( L-CH) and
VR10 (R-CH).
(See fig. 1.)
2) Repeat steps 5 and 6 for
conf irmation (Proceed to
steps 7, 8 and 9 if the
curve is now within the
charted spec ifications as shown fig. 10.)
3) If the curve still exceeds the specifications (fig.
10), increase bias current further and repeat
steps 5 and 6.
7. Place UNIT into CrO
2
8. Change test tape to CrO
(QZZCRX), and record 1 kHz, 50 Hz, 100 Hz, 200 Hz, 500 Hz,
4 kHz, 8 kHz, 10kHz and 15 kHz signals.
the signals and check if the curve is within the limits
shown in the overall frequency response chart for CrO
tapes (fig. 14).
9. Place UNIT into metal tape mode and change test tape to
metal reference blank test tape (QZZCRZ), and record
1 kHz, 50 Hz, 100 Hz, 200 Hz, 500 Hz, 4 kHz, 8 kHz, 10 kHz, _
12.5 kHz and 15 kHz signals. Then, playback the signals _ 4d8
and check if the curve is within the limits shown in the
overall frequency response chart for metal tapes (fig. 14).
10. Confirm that bias currents are approximately as follows
when the UNIT is set at different tape mode.
• Read voltage on VTVM between ground anrl test point
(TP1 for L-CH, TP2 for R-CH) and calculate bias current by following formula :
.
Bias current
(A) =
Standard value : around 500µA (CrO
.,
,,,
-
+3dB
+2dB
OdB
2dB
3dB
I 3 11.5 kHz
2
kHz kHz kHz
1
I0kHz
4 kHz
5 kHz
9kHz
6kHz )kHz 8kHz
Fig. 1 2
tape mode.
2
reference blank test tape
Then, playback
Value read on VTVM (V)
10 (Q)
around 400µA (Normal position)
2
position)
around 800µA (Metal position)
Overall frequency response chart (Normal)
+6dB
+ 4 d B
+ 2dB
ods
- 2 d B
- 4 dB
,I
-6dB
63Hz I 00 Hz 200 H z
Record/
playback­
head
Adjustment (B) :
When the curve falls below
the overall specified fre­
quency response chart (fig.
10) as shown in fig. 13.
1) Reduce bias current by
turning VR9 (L-CH) and
VR10 (R-CH).
2) Repeat steps 5 and 6 for
confirmation (Proceed to
steps 7, 8 and 9 if the
curve is now within the
charted spec ifications as
shown fig. 10.)
3) If the curve still falls below the charted specifica­
tions (fig. 10), reduce bias current further and
repeat steps 5 and 6.
Overall frequency response chart (CrO2, Metal)
2
+ B dB
+ 4 dB
+ 2 d8
O dB
2 d 8
,,
- B d B
50 Hz 1 00 H z 200 Hz
- 8 -
-
_,,.v
�
........
......
500Hz ! kH z 2 k H z 5 kHz I 0 k Hz 1 2 5 k Hz
Fig. 1 0
esponse measurement
For bias voltage
measurement
Fig. 1 1
-
-
+3dB
-
... +2dB
l
I kHz 1kHz 3kHz \ 11.5 kHz
4kHz
I0kHz
5 kHz 9kHz
6kHz 7kHz 8 kHz
Fig. 1 3
- -
�
.,,-
/
�
........
r-
,-.
500Hz 1 kHz 2 k H z 5 k H z 1 0 kHz 1 5 kHz
Fig. 1 4
+ 3 dB
+ 2 dB
OdB
2dB
-3dB
dB
2dB
3dB
+ 4 .5dB
+ 4 dB
+ 2dB
OdB
2dB
- 4 d B
- 4 . 5 dB